I will explain how a man lived 150 years or more in pre-historic days of Oldteatament. One day is counted as time taken by earth for one revolution. If a man can live 100 years the life span of a man is "100 yrs X 365 dys X 24 hrs". Recently some two years ago do you remember "1 second" was adjusted in Newyear day. That is due to slowness of earth revolution. These type of adjutsments are made scientifically now. You assume that the eath was revolving faster than now in pre-historic time such that the time taken for one revolution of earth is "12 hrs only". So the total time span of man of 100 years now is equal to 200 years then, that is "200 yrs X 365 dats X 12 hrs. That is how a man in old testament days lived more than 100 years and it is going on coming down. It is due to increase in mass and size of the earth going on increasing. There is history of some small planets have fallen on this earth and created earth quakes and Floods. Do you knoe fire of Siberia for more than 100 years due to fall of a celestial body. So the size of earth in increased and the rotation speed is reduced. That is why men's life span reduced to 100 years and less. It was more in olden days due to more speed in rotation of earth.